As there's manual input ( button push ), you could use millis() of the first button press as a random seed, too. Or simply call random(); in the beginning of loop() where now is your randomSeed(), this will be repeated an undefinite number of times, until both buttons are pressed.

BTW: Your code does not generate a sequence at all, as it never ends the loop().Strange design... you need to press 3 buttons: Reset, then the 2 others together.